1. Field of the Invention
The present invention relates to a printing device for printing images on a web.
2. Description of the Related Art
A printing device that performs both-side printing by continuously transferring a long web and making two individual printing units perform printing on the front side and the back side of the web has been known.
When such a printing device performs one-side printing on the web, only one printing unit is used for printing. This decreases printable-page productivity in one-side printing compared to that in both-side printing.
Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 2007-50600) discloses an image forming system that has two image forming devices to perform one-side printing on each continuous paper (web) and thus maintains the same productivity as that in both-side printing.
The image forming system in Patent Literature 1 has two image forming devices arranged in the shape of the letter L. In both-side printing, continuous paper is wound around a turn bar arranged between the two image forming devices so that the paper is turned over to have its travel direction changed by 90 degrees. This allows a first image forming device to print on the front side of the continuous paper fed by a first continuous paper feeder, which is arranged upstream of the first image forming device, and allows a second image forming device to print on the back side of the continuous paper. The both-side printed continuous paper is cut and stacked at a second after-treatment device arranged downstream of the second image forming device.
In one-side printing, the first image forming device prints images on one side of continuous paper fed by the first continuous paper feeder, and the one-side printed continuous paper is cut and stacked at a first after-treatment device arranged downstream of the first image forming device. The second image forming device prints images on one side of another continuous paper fed by a second continuous paper feeder, and the one-side printed continuous paper is cut and stacked at the second after-treatment device arranged downstream of the second image forming device. This enables the first image forming device and the second image forming device to individually perform one-side printing in parallel to maintain the same productivity as that in both-side printing.
However, since the image forming system in Patent Literature 1 performs printing on one sheet of web (continuous paper) in both-side printing and two sheets of web in one-side printing, a user is required to replace the web sheets when switching between the one-side printing and the both-side printing, which takes much time and labor.